Mobile phones are not provided with a pointing device such as a mouse or a trackball, because portability is critical to mobile phones. Accordingly, it is difficult to select an icon displayed on a screen of a mobile phone, as compared with a personal computer, which has a pointing device. To address such a problem related to operability, for example, patent document 1 describes displaying plural icons on a screen such that they have the same arrangement as keys of a numeric keypad; activating an icon that is in the same position in an array as a pressed key; and displaying a number of a corresponding key on each icon. Alternatively, patent document 2 describes, as shown in FIG. 4 thereof, assigning to a “tree” object OBJ4 positioned at block B (4, 3) of an image displayed on a mobile phone, which image is divided into a matrix of four rows and three columns in the same way as keys of the phone, a function of starting a game and a key which is arranged at a position corresponding to block B (4, 3), and if the key is pressed, selecting object OBJ4 to start a game. Alternatively, patent document 3 describes dividing an image displayed on an LDC into plural areas arranged in the same way as keys of a numeric keypad, and enlarging an image in an area corresponding to a pressed key.    Patent document 1: JP-A-2004-179870    Patent document 2: JP-A-2005-216170    Patent document 3: JP-A-2005-175977
Based on the inventions described in patent documents 1 to 3, it is possible to conceive of selecting a window from among plural windows displayed on a screen. However, windows are different from icons described in patent document 1 and objects described in patent document 2, in that a size and a position can be freely changed by a user on a screen. Accordingly, if a configuration of displaying plural windows on a screen in the same array as keys of a numeric keypad, as in the case of icons described in patent document 1, is employed, it is necessary to change a size and a position of each window as determined by a user. However, since a size and a position of each window have been arbitrarily determined by a user to make them easy to use, if they are automatically changed, a user has to again change a size and a position of each window in accordance with the user's preference. Also, if a configuration of assigning a key of a numeric keypad to each window in advance, as in the case of objects described in patent document 2, is employed, and if a position or a size of a window is changed, a correlation between positions of windows on a screen and an arrangement of keys of the numeric keypad is lost. As a result, it becomes unclear which key is to be pressed; namely, operability is lowered.
Also, if a configuration of dividing a displayed area into plural areas arranged in the same way as keys of a numeric keypad, and selecting a window displayed in an area corresponding to a pressed key is employed, and if plural windows are displayed in an area corresponding to a pressed key, it is impossible to identify which window is to be selected.